Host & Domain from same provider?

That's an interesting question, and my answer would have to be the same as yours; I would never purchase a domain from the same provider as my host. While it is generally fine to do so, if you decide to switch providers away from their registrar or webhosting services, you can run into a slew of problems - especially if the provider is desperate enough to look to keep customers by any means necessary. It's true, you never know when one or the other will go out of business, too. If you choose a reputable company, I don't see how there is likely to be any issues with this, but I keep them separate just in case.